FGFS-4.1/simgear
3
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Make base64 decode significantly faster.

Browse Source 
Use a reverse lookup table instead of a call to string.find for
each input byte, much speedier.
This commit is contained in:
James Turner
2013-10-05 23:24:51 +01:00
parent 0bd82a43d3
commit 68cd84c330
1 changed files with 20 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
simgear/misc/strutils.cxx
View File

@@ -344,7 +344,24 @@ static const std::string base64_chars =
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";
static const unsigned char base64_decode_map[128] =
{
127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
127, 127, 127, 62, 127, 127, 127, 63, 52, 53,
54, 55, 56, 57, 58, 59, 60, 61, 127, 127,
127, 64, 127, 127, 127, 0, 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 127, 127, 127, 127, 127, 127, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
49, 50, 51, 127, 127, 127, 127, 127
};
static inline bool is_base64(unsigned char c) {
return (isalnum(c) || (c == '+') || (c == '/'));
}
@@ -375,7 +392,7 @@ std::string decodeBase64(const std::string& encoded_string)
char_array_4[i++] = encoded_string[in_]; in_++;
if (i ==4) {
for (i = 0; i <4; i++)
char_array_4[i] = base64_chars.find(char_array_4[i]);
char_array_4[i] = base64_decode_map[char_array_4[i]];
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
@@ -392,7 +409,7 @@ std::string decodeBase64(const std::string& encoded_string)
char_array_4[j] = 0;
for (j = 0; j <4; j++)
char_array_4[j] = base64_chars.find(char_array_4[j]);
char_array_4[j] = base64_decode_map[char_array_4[j]];
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);